Social interactions among a mother, an adopted infant, and a real infant were studied in Japanese macaques (Macaca fuscata) during 5-9 months of t he infants' life, compared with mother-single infant interactions. In 1987, one multiparous female in a provisioned group adopted a non-related male baby, one day after her birth of a male baby. The mother took care of the adopted infant in the same way with her real infant. Nipple contact of each infant was synchronized. When both infants were in nipple contact, the mother less frequently rejected it and less frequently left the infants, and the infants also less frequently left the mother, than they did so when either infant was in nipple contact. This indicates that the mother nursed both infants at a time, to reduce the total nipple contact time, and to increase other activities such as feeding and social interactions with other individuals. The infants might contribute the synchrony, to increase their own nipple contact time, in accordance with such tactics of the mother. This shows one case that Japanese macaques have the potential ability to modify their behavior pattern in a certain social environment.

抄録全体を表示

Effects of the presence of older sibling on the social relationships of juveniles with other monkeys were assessed in a free-ranging group of Japanese monkeys at Katsuyama, Okayama Prefecture, by comparison between fifteen 2-year-old juveniles with older siblings (3-6year old) and nine 2-year-old juveniles without older siblings. The juveniles' proximity and playmate relationships with other monkeys in the group were analyzed in a situation where the juveniles were apart more than 2m from their mothers. The juveniles without older siblings tended to maintain more frequent proximity relationships with same-aged monkeys than did the juveniles with older siblings, while the juveniles with older siblings were in more frequent proximity with adults than did the juveniles without older siblings. These results suggest that the juveniles with older siblings had more opportunities to interact with elder monkeys through agent of their older siblings than did the juveniles without older siblings. The juveniles without older siblings tended to interact more frequently with same-aged monkeys than did the juveniles with older siblings, due to the lack of such opportunities. The male juveniles with older brothers and the female juveniles with older sisters were in more frequent proximity with each other than were those who had the older siblings of the opposite sex. The male juveniles had opportunities to interact with elder males, when they were in proximity with their older brothers.

抄録全体を表示

In order to investigate the possible role of the prefrontal association cortex (PFC) in the periphe ral visual attention, we examined the neuronal activities in the PFC while the monkey is performing a visual attention task (VAT) and a visual fixate a small spot was dimmed in the VAT. While recording sessions, these tasks were tested in blocks. It was confirmed that the monkey is using different attent ive state in two task conditions by measuring the reaction time of the very first trial of each block. Visual responses of 81 neurons were analyzed in detail. Of these, 53% were either enhanced (25%) or suppressed (27%) during the VAT. In 43 neurons, activities during saccade toward thestimuluspresented within the receptive field was also tested. Of these, 25 neurons showed pre-saccadic activities (saccadic neurons) and 18 neurons showed no pre-saccade activities (non-saccadic neurons). Among the saccadic neurons, activities of 68% were modulated during the VAT. Ammong the non-saccadic neurons, 61% were modulated during the VAT. These results suggests that the PFC is involved in the visual information processing, such as, selecting the relevant visual stimuli in the visual world without eye movement as well as with eye movement.

抄録全体を表示

The present study aimed to clarify the feeding behavior of captive chimpanzees on planted trees in their enriched environment. A group of nine chimpanzees was kept in an about 700 square-meters semi-natural compound with a climbing structure, planted trees, a stream, and so on. The outdoor compound was connected to the other two outdoor compounds and the indoor facilities of experimental rooms and sleeping places. As a project of planting trees for captive chimpanzees, we planted a total of 140 trees of 28 species in the compound. The trees were about 50cm to 3m tall and were fixed by bamboo sticks in the ground. The fixation successfully prevented the chimpanzees pulling out the trees. We checked in a regular interval the feeding behavior of chimpanzees to the planted trees. The chimpanzees showed high selectivity in feeding behavior. They almost ate up the trees like Quercus myrsinaefolia, Quercus serrata, Eriobotrya japonica, Elaeagnus umbellata, etc. They ate to some extent the trees like Rhododendron indicium, Weigela coraeensis, Osmanthus fragrans, etc. They never ate the trees like Aucuba japonica, Spiraea thunbergii, Camellia japonica, Camellia sasanqua, Hydrangea macrophylla, etc. In general, the chimpanzees never ate coniferous trees but ate some of the broad leaf trees. They preferred deciduous trees to evergreen trees. There were also grasses naturally grown in the compound. The chimpanzees spent about 40% of the feeding time to eat the grasses. They showed marked preference to the family of Gramineae but they did not eat the family of Compositae. The present study indicated an effort of the environmental enrichment by planting trees. This provided the rare opportunity for the chimpanzees to perform a variety of free feeding behavior essential for their lives in the natural habitat.

抄録全体を表示

The Seibu Road runs through the Natural World Heritage area of Yakushima Island, Japan. The volume of traffic and velocity of cars using the road were investigated in February, 1995. During daytime (8:30-17:30), 32 cars used this road on average (range 29-37 cars). One-fourth of them were considered to be tourist traffic. The velocity of cars running along the road was 33km/hr on average (range 21-52km/hr) where the road width was thinnest (4m). Judging from the traffic volume of the road, setting a speed limit for cars of 20km/hr would be sufficient for road safety. Intensive construction work for widening the road width is not required for safety. Moreover, it will greatly damage wildlife and the natural environment of the World Heritage.

抄録全体を表示